In the conventional manufacture of synthetic textile yarns, a molten polymeric material is extruded in the form of multiple continuous filaments which, after quenching to cool the filaments below their glass transition temperature, are gathered and transported longitudinally in an indeterminate length coextensive bundle commonly referred to as a tow. A driven take-up unit disposed downstream of the extruding apparatus delivers the tow at a controlled transport speed to a canning station at which the tow is deposited into an open-top can or similar container for storage and, in some cases, transportation to another site for further processing.
In a typical drawing operation, tows from a plurality of the filled cans are placed in a common creel for delivery and processing in side-by-side parallel warp sheet form through a draw frame to subject the tows simultaneously to a stretching and heat setting operation to orient the molecular structure of each constituent filament in each tow. Following the stretching and heat setting steps, the tow usually is chopped into staple lengths from which yarn can be spun. Prior to spinning, the staple length tows often are subjected to a carding process to restore uniformity to the material that may be lost during chopping.
In a typical operation, the indeterminate length tow is continuously fed from the container to the stretching and heat setting equipment until the container is emptied. The process is then interrupted, while the leading end of a tow from a new container is joined to the trailing end of the tow from the emptied container by manually sewing the tow ends together. This manual splicing process is sometimes referred to as lacing. FIG. 1B illustrates a tow splice form by lacing.
Once the ends of the new tow and expiring tow are joined, stretching and heat setting processes are resumed. In one typical stretching process, the tow is engaged by a first roller rotating at one rate (e.g., 100 rpm), followed by a closely-spaced second roller rotating at a relatively higher rate (e.g., 300 rpm). Such rollers subject the tow splice to forces on the order of 1,200 lbf. The splice needs to be of sufficient strength to keep the tow ends together during the stretching and heat setting processes. Otherwise, the equipment needs to be shut down to resolve the splice failure, resulting in additional downtime.
The present lacing technique for joining indeterminate length tow ends suffers from several drawbacks. For one, the process is labor-intensive and time-consuming, requiring significant downtime. Another drawback is that a relatively large area of overlap is needed to form a splice having sufficient strength to withstand the ensuing stretching and heat setting operations. This large area of overlap leads to a higher occurrence of inferior quality (or unusable) fiber due to the fibers in the area of the splice not being sufficiently stretched and heat-set. Yet another problem with lacing is the occurrence of so-called wraps, which refer to small portions of the unwoven tow becoming entangled in the rollers of the stretching machine. When this occurs, it is necessary to interrupt operation to clear the entangled tow, producing yet more costly downtime. Lacing also can have result in hard (more dense) areas in the stretched and heat-set staple tow product. The equipment used in many types of downstream textile operations can be sensitive to these hard areas, resulting in production irregularities and/or damage to the equipment.
It would be desirable to develop an alternative technique for joining fiber tow ends, especially one that can be completed in less time than is required for present lacing techniques. It would be desirable to produce splices of consistently high quality, so as to reduce the occurrence of splice failure and associated interruption of the stretching and heat setting or other downstream operations. It also would be desirable to reduce the amount of inferior quality fiber produced due to the large area of overlap needed for the splice in present lacing techniques.